1. Field of the Invention
The present invention generally relates to a communication message conversion device, a communication method and a communication system, and in particular to a communication message conversion device, a communication method and a communication system to be connected to different communication protocol channels.
2. Description of the Related Art
In recent years, the number of electronic equipment to be mounted in vehicles is increasing, and an in-car LAN is being widely used to prevent the increase in the number of wire harnesses for connecting such electronic devices.
For example, with the in-car LAN, the application nodes of Electric Control Units (ECU) and the like provided to the engine control device, transmission control device, and control devices for ABS, dashboard indicators, lights and power windows are connected communicably, and various controls are performed thereby.
FIG. 11 shows a conventional application node employing in an in-car LAN. This application node 100 is connected to a LAN transmission channel 130 such as an in-car LAN, and communicates with the other application nodes 100 via this LAN transmission channel 130. Further, the application node 100 comprises, as illustrated in FIG. 11, a control unit 110 and a communication control unit 120. Moreover, the control unit 110 comprises an application processing unit 111 and a message handling unit 112.
The communication control unit 120 is a communication controller or the like, and enables the communication with other application nodes 100 via the LAN transmission channel 130 according to a communication protocol. For instance, the communication control unit 120 receives a frame from the LAN transmission channel 130 and analyzes the message, and stores the received message in the register of the communication control unit 120.
The control unit 110, for example, is configured by a CPU executing processing according a prescribed program, and cooperating with other hardware.
The message handling unit 112 performs processing based on a transmission/receiving task or the like, and relays the message between the communication control unit 120 and the application processing unit 111. For example, the message handling unit 112 reads the received message from the register of the communication control unit 120, and stores this in the message buffer of the control unit 110.
The application processing unit 111 performs processing based on an application task or the like, and performs the various applications of the application node 100, and performs processing according to the generation of an transmitting message to the other application nodes 100 and the message received from other application nodes 100. For instance, the application processing unit 111 acquires the received message via the message buffer of the control unit 110.
Further, the transmission/receiving task and application task may be scheduled with an OS (not shown), and the respective tasks may be dispatched and executed thereby.
Meanwhile, Controller Area Network (CAN) is known as one of such in-car LANs. The CAN communication system employs a CSMA/CA system, and, when the transmission channel is open, all application nodes are able to transmit a message, and, when the message of other application nodes is flowing in the transmission channel, the other message cannot be transmitted. Specifically, CAN is adopting an event-driven communication system that issues a communication request in accordance with the generation of an incident, and enables transmission only when the transmission right has been obtained. For example, a conventional system employing CAN is disclosed in Japanese Unexamined Patent Application Publication No. 2003-264567.
FIG. 12 is a diagram for explaining the timing operation in the case of employing the application node 100 illustrated in FIG. 11 in CAN. Since CAN is event-driven, a frame is flowing in the CAN transmission channel at odd intervals, and not in a constant cycle as shown in FIG. 12. The frame of CAN contains the SOF (Start Of Frame) representing the start of the frame and EOF (End Of Frame) representing the end of the frame. The communication control unit 120 detects and synchronizes the frame by detecting the SOF, and then receives such frame.
As shown in FIG. 12, when the communication control unit 120 receives the frame, it notifies the frame reception by interrupting the transmission/receiving task, and the transmission/receiving task is executed upon such interruption. And, the transmission/receiving task reads the received message, and stores it in the message buffer.
As shown in FIG. 12, the application task is executed upon storing the received message in the message buffer, and prescribed processing is performed. As described above, the scheduling systems of the transmission/receiving task and application task are also event-driven to match the communication system of CAN, and processing according to the frame flowing at odd intervals in CAN is executed.
Contrarily, FlexRay is attracting attention as a communication protocol that is more reliable than CAN. For example, FlexRay is described on page 115 to 122 of an article entitled “This is ‘FlexRay’—the Fast and Reliable In-Car LAN” by Andreas Both and Michio Sato, in “Nikkei Electronics” issued by Nikkei BP on Feb. 2, 2004. FlexRay is adopting the time-trigger communication system which hardly generates delay communication in communication in order to improve reliability. Further, the transmission rate of FlexRay is 10 Mbps at maximum, and, in comparison to the 1 Mbps of CAN, is capable of high-speed communication.
FIG. 13 is a diagram for explaining the flow of the timing operation in a case of employing the application node illustrated in FIG. 11 in FlexRay. As shown in FIG. 13, with the FlexRay transmission channel, the transmission/receiving of frames is conducted based on a time slot partitioned in a prescribed time. For example, as a result of predetermining the time slot to be used by the application node for transmission, the delay variation in communication can be prevented and the bandwidth is guaranteed thereby.
The communication control unit 120 detects the time slot with a timer synchronized to the global time on the network and receives the frame from a prescribed time slot.
As shown in FIG. 13, the execution time of the transmission/receiving task is managed with the timer as used in the communication control unit 120, and the transmission/receiving task is executed at a predetermined time. If the receiving message has arrived at the communication control unit 120 when the task was executed, the transmission/receiving task reads such received message, and stores this in the message buffer. As shown in FIG. 13, the application task is similarly executed at a predetermined time as the momentum, acquires the received message from the message buffer, and prescribed processing is performed thereby.
As described above, the scheduling systems of the transmission/receiving task and application task are also basically time-triggered to match the communication system of FlexRay, and processing according to the frame periodically flowing in FlexRay is often executed.
As described above, with a control unit (application node) configuring a conventional vehicle control system, a system (CAN for instance) of synchronizing with the event and arbitrating the communication collision among the units was dominant. In such a case, a reliable and efficient system was created by giving priority to the control operation of the control unit. Meanwhile, the amount of information communicated among the units has continued to increase due to demands of sophistication of the control system. Further, the information exchanged via the communication channel which was initially auxiliary information, is now becoming information having a significant influence on the operation of control as well as the safety of the vehicle. This kind of qualitative change of information will most likely become greater in the future.
In a conventional communication system, when introducing a time-triggered communication protocol (such as FlexRay) in order to improve the reliability of the dispersive real-time control system, secure the network bandwidth, and determine the amount of delay, it is difficult to divert the existing system and control software and development technology designed for an event-driven communication protocol (such as CAN).
In such a case, in order to make a transition from a conventional event-driven task control system to a time-driven task control system, much time and cost will be required for the significant design change in the system and for the broad reexamination procedures.
Particularly in a power drive control system or motor control system of vehicles requiring high reliability, since the influence of not being able to succeed the software assets created from the past is significant in the majority of the control units, this was a factor in preventing the introduction of new communication technology.
The following drawbacks will arise when adopting the conventional technology capable of realizing the foregoing functions in the present technical field. For example, since the data size of the payload is often smaller than the data size of the message frame management information, when the conventional technology is employed, the transmission efficiency focusing on the payload will become inferior, and the transmission rate of the payload will decrease. Further, when simultaneously using the conversion of the management information (message header), this is substantially difficult since high processing power in comparison to communication processors available in this field will be required, or an extremely large memory must be prepared.
As described above, with a conventional communication system, when a device operating under an event-driven communication protocol tries to use a different communication protocol such as a time-triggered communication protocol, in addition to the diversion of existing configurations being difficult, problems such as deterioration of the transmission efficiency and necessity of high power devices would arise.